EP0846378A1

EP0846378A1 - Method and device for spatial multiplexing-demultiplexing of radio signals for an sdma mobile radio system

Info

Publication number: EP0846378A1
Application number: EP96929359A
Authority: EP
Inventors: Joel c/o Thomson-CSF SCPI THIBAULT; Pascal c/o Thomson-CSF SCPI CHEVALIER; François c/o Thomson-CSF SCPI PIPON; Jean-Jacques c/o Thomson-CSF SCPI MONOT; Gilbert c/o Thomson-CSF SCPI MULTEDO
Original assignee: Thomson CSF SA
Current assignee: Thales SA
Priority date: 1995-08-22
Filing date: 1996-08-22
Publication date: 1998-06-10
Anticipated expiration: 2016-08-22
Also published as: US6240098B1; DE69604595D1; DK0846378T3; DE69604595T2; WO1997008849A1; EP0846378B1

Abstract

The method of the invention, which uses a multichannel transmitter and receiver (1) integrated in a base station and coupled to an antenna array, includes, for digital radio signals containing previously known or non Gaussian sequences and arranged in frames, estimating (2) the spatial information about each mobile unit on the basis of the signal received by the receiver for the reception and transmission frequencies, by means of said known sequences or by means of blind source separation methods, and, from this information, isolating (3) by spatial filtering in the presence of multiple channel paths the respective paths of each mobile unit with a power above a predetermined threshold, in order to provide spatial demultiplexing, and simultaneously transmitting in the direction of the main path of each mobile unit the signal intended for it, while protecting each mobile unit from signals transmitted in the direction of other mobile units by spatial filtering with cancelling constraints, in order to provide spatial multiplexing. The invention is useful for cellular radio communications.

Description

METHOD AND DEVICE FOR SPATIAL MULTIPLEXING / DEMULTIPLEXING RADIOELECTRIC SIGNALS FOR RADIO MOBILE SDMA SYSTEM

The present invention relates to a method and a device for spatial multiplexing / demultiplexing of radio signals organized in frames and transmitted in duplex on the same frequency and time channel which does not require calibration. It applies, in particular, to cellular radiocommunications between at least one base station and several mobiles.

With the constant increase in the demand for mobile communications and the limitation of the number of channels allocated to operators of cellular radiocommunication networks, the problems of saturation will become crucial in the years to come. Conventional techniques currently make it possible to multiplex communications in frequency (TDMA), in time (TDMA), or in code (CDMA).

AMRF (Frequency Distribution Multiple Access) consists in allocating to each communication a pair of frequencies (one for the downlink and one for the uplink). All by itself, this very simple multiplexing technique offers almost no prospect of improving spectral efficiency.

AMRT (Multiple Access to Time Distribution) consists in allocating a precise time interval to each communication. Only this technique, already optimized for improving spectral efficiency in the context of speech transmission by exploiting the silences present on the speech signal, suggests little additional improvement in this area.

AMRC (Multiple Access to Distribution in Codes) consists in allocating a code to each communication, defining a frequency hopping law over short time intervals. Even if it allows a certain increase in spectral efficiency (progressive saturation by degradation of the signal and not abrupt by interruption of the service as in the case of the two previous techniques), this method remains cumbersome and expensive to implement. Several avenues are currently being explored to improve the capacities of cellular communication systems, namely: the diversification of cells and waveforms with the implementation of cells of increasingly reduced sizes frnicroceir'et tιanocell "of the standardization project ATDMA, English abbreviation for "Advanced Time Division Multiple Access", for urban areas), and above all a new multiplexing method that can be combined with existing techniques: Multiple Spatial Distribution Access (AMRS or SDMA in English terminology) This technique is based on the idea that the radio signals corresponding to several links between a base station and mobiles can in many cases be spatially decorrelated.

The use of this decorrelation makes it possible to separate the space channels (even if they all occupy the same frequency and time channel) by means of a multi-channel transmission / reception system associated with a base of antennas adapted to the frequency range used. .

Several methods implementing this concept have already been proposed. A first method is based on arrival direction estimation techniques such as the system described in the patent of Richard ROY (US Patent PCT / US92 / 10074, 12/1991, entitled 'Spatial Division Multiple Access Wireless Communication System') . A second method uses cyclostationary characteristics of digital transmission signals to separate them by blind processing (US Patent No. 5,260,968, of 9/11/93, entitled Method and Apparatus for Multiplexing Communications Signais through Blind Adaptative Spatial Filtering "by William A. GARDNER and Stephan V. SCHELL).

For the first method, the estimation of the directions of arrival of different radio sources from the signals received on a base of antennas, requires perfect control of the wavefront which results in a calibration constraint of the base of antennas used. In addition to the additional cost induced by the calibration, the standard deviation of the indirect estimate of the director vector from the estimated direction of arrival and from the calibration table of the antenna base is significantly greater than that obtained by direct estimation methods. The directing vector corresponds to the value taken by the base transfer function antennas for the azimuth, the site and the carrier frequency of the incident electromagnetic wave emitted by a source. This information is then used by the spatial multiplexing processing.

For the second method, the order 2 separation techniques using cyclostationarity impose on the signals to be separated either differences in symbol rhythms or shifts in carrier frequencies in order to function. These limitations make these techniques unsuitable for the configurations of channels formed in radiocommunications between a base station and mobiles having uncorrelated multipaths which are not separable by the previous methods and therefore non-operational in most urban areas.

Finally, the antenna processing techniques mentioned above, implement to separate the different signals received a so-called purely spatial filtering structure constitutes a complex gain per reception channel. The anti-jamming capacities of this type of structure in terms of the number of independent rejectable jammers (two decorrelated paths originating from the same source constitute two independent jammers) are suboptimal. Indeed, the spatial filter adapts to a useful path followed by a source and rejects all the other paths, both the decorrelated useful paths followed by this source and the paths followed by the interfering signals.

In the following description, the terms "sensors" and "antennas" will be used interchangeably as well as the terms "multi-sensor", "multi-channel", and "multi-sensor network" and antenna base ", knowing on the other hand that an antenna base, or multisensor network, forms a number of transmission channels equal to the number of antennas, or of sensors.

The invention aims to overcome the imperfections and limitations of the above methods.

To this end, the subject of the invention is a method for spatial multiplexing / demultiplexing of radio signals organized in frames and transmitted in duplex between at least one base station and several mobiles communicating on the same frequency and time channel by means of a receiver and a multi-channel transmitter integrated in the base station and coupled to an antenna base.

A first variant of the invention applies particularly to non-Gaussian radio signals. The process which is the subject of this first variant is characterized in that it consists:

- to estimate the spatial information relating to each mobile from the signal received by the multi-channel receiver, for the reception and transmission frequencies, by means of blind source separation methods, and from this information, - to isolate by spatial filtering, whether or not there are multiple paths in the channel, the respective paths to each mobile whose power is greater than a determined threshold to allow spatial demultiplexing, and

- to transmit simultaneously, in the direction of the main path of each mobile, the signal intended for it, by protecting each mobile from signals transmitted to others by spatial filtering with cancellation constraints to allow spatial multiplexing.

A second variant of the invention applies to digital radio signals organized in frames comprising sequences known a priori. The process which is the subject of this second variant is characterized in that it consists:

- to estimate the spatial information relating to each mobile, from the signal received by the multi-channel receiver, for the reception and transmission frequencies, by means of filtering methods, by exploiting the sequences known a priori, and from of this information, - to isolate, in the presence or not of multipaths in the channel, the respective paths to each mobile whose power is greater than a determined threshold, and to demodulate the signal received from each of the mobile in connection with the station base, to allow spatial demultiplexing, and

The invention has several advantages.

An advantage of the first variant of the present invention is to allow, for the estimation of the guiding vectors associated with the different mobile signals, to apply a blind source separation method that does not require control of the wavefront or prior knowledge of the waveform (transparent method). The method according to the first variant of the invention exploits for this the non-Gaussian character of the source signals. This assumption is verified for most of the modulations used in analog or digital radio communications, in particular for constant envelope modulations.

An advantage of the second variant of the invention is to allow, for the spatial multiplexing of radio transmissions between several mobiles and a base station, techniques for adapting spatial or space-time filters on replica (sequence of learning) so far mainly implemented for anti-jamming in defense radiocommunication systems. Most digital cellular radio systems use, for synchronization and equalization needs in particular, training sequences inserted in waveforms organized in frames. The use of this information, known a priori, allows the implementation of more efficient and less restrictive treatments in terms of the modulations used than the so-called "transparent" techniques.

Among the methods described below, during the description of the second variant, those implementing spatio-temporal filtering structures (one FIR filter per channel, Anglo-Saxon abbreviation for "Finite Impulsional Response"), allow in the presence multipaths, to increase the rejection capacities of interfering signals and to optimize the error rate after demodulation of a multichannel system compared to narrow band filtering structures (one coefficient per channel); control of the wavefront is not necessary, which allows the use of an uncalibrated antenna base; and compatible modulations of these methods encompass all digital modulations including Gaussian waveforms.

Other advantages and characteristics of the present invention will appear more clearly on reading the description which follows and the appended figures which represent: FIG. 1, the main steps of the method according to the invention,

FIG. 2, a functional diagram of a device for implementing the method according to the invention,

FIG. 3, an example of the structure of a "superframe" taking into account the constraints of the AMRS mode,

- Figure 4a, a functional diagram specifying the interface between the AMRS controller and the estimation and spatial multiplexing / demultiplexing means, according to the second variant of the invention, - Figure 4b, a functional diagram specifying the interface between the AMRS controller and the spatial estimation and multiplexing / demultiplexing means, according to the first variant of the invention,

- Figure 5, a diagram of the decomposition of a frequency and time channel into spatial subchannels, - Figure 6, an illustration of the concept of frequency and time channel,

FIG. 7, a table of spatial correlation of the mobiles present in the cell (taken two by two), and

- Figure 8, a block diagram of a switching and calibration module of the device for implementing the method according to the invention.

- Figure 9, a multi-sensor spatial filter structure + single-sensor equalizer / demodulator, according to the second variant of the invention, - Figure 10, a general structure: multi-sensor space-time filter + single-sensor equalizer / demodulator, according to the second variant to the invention,

FIG. 11, a first implementation corresponding to a transmission channel of the general structure of FIG. 10 entitled FAST-BBT-DFE, according to the second variant of the invention, and

- Figure 12, a second implementation of the general structure of Figure 10 called FAST-DFE, according to the second variant of the invention. In the figures, the homologous elements are designated by the same reference.

The method according to the first variant of the invention, the main steps of which are illustrated in FIG. 1 consists, from a multi-channel transmission / reception 1, of estimating 2 the spatial information concerning each active mobile source present in the cell at both frequencies, transmission and reception supports alternately, then from this information to achieve an optimal global multiplexing / demultiplexing 3 (time, frequency and space) of the communications. The spatial information characterizing a mobile is defined by the directing vectors of the multipaths of the signal received on the basis of antennas.

These guiding vectors represent the response (amplitude and phase) of the antenna base to an incident signal along an azimuth characteristic of the position of the source. The estimation 2 of the guiding vectors of each source uses signals received from the source of interest in a single-emission configuration. In other words, in the waveform organized in frames, a periodic time range, hereinafter called "burst", is allocated to each mobile for updating its spatial information. The method applied for this estimation 2 therefore exploits the non-Gaussian nature of the source signals to be processed and works perfectly in the absence of calibration of the antenna base. On the other hand, given the generally large difference between the frequencies of the uplink (mobile to base station) and downlink (base station to mobile) frequencies, the estimate made on the received signals and used for spatial filtering reception cannot be transposed for spatial filtering in transmission. This is why, in the method according to the first variant of the invention, a periodic permutation of the frequency groups of the uplink and downlink can be carried out so as to allow learning and updating of the spatial information also at the frequencies d 'program.

Most base stations manage several frequency channels in duplex mode and in this context the method according to the first variant of the invention can make it possible to ensure overall management of these channels within which spatial multiplexing generates AMRS subchannels so as to group preferentially on the same frequency and time channel the mobiles least spatially correlated.

In addition, the method according to the first variant of the invention updates the coefficients of the spatial filters in reception and in transmission, performing respectively a spatial demultiplexing and a spatial multiplexing by taking into account the pairing faults, consequence of residual errors of taring of transmission and reception channels.

A device for implementing the method according to the first variant of the invention is shown diagrammatically in FIG. 2 and includes the following sub-assemblies:

a base of antennas 4 coupled to means 5 for frequency switching and setting,

a multi-channel receiver 6 comprising radio transposition / amplification means, and multi-channel analog / digital conversion means not shown,

- a space demultiplexer 7,

- a determined number of demodulators 8i equal to the maximum number of spatial channels fixed per frequency channel, for example three demodulators for a base comprising ten antennas, - a multi-channel transmitter 9 comprising means of radio transposition / amplification and multi-channel digital / analog conversion not shown,

- a spatial multiplexer 10,

a determined number of modulators 11 i equal to the number of demodulators 8i of the multi-channel receiver 6,

- a digital processing module 12, delimited by a closed line in broken lines, comprising a controller 13 and an estimator 14 specific to the AMRS processing, which is at the heart of the device for implementing the method according to the first variant of the invention. The implementation of the concept of AMRS by means of blind source separation methods, by the equipment it requires, the constraints of the treatments applied and the new possibilities it offers, requires system consideration. This results in a number of control and management tasks essential for optimal integration of spatial multiplexing in the radio communication networks. These control and management tasks are performed in the device for the implementation of the method according to the first variant of the invention by the digital processing module 12. The separation, at the base station, of the signals coming from or for the various "active" mobiles, that is to say in communication with the base station, in a given cell, involves the acquisition and updating of the specific spatial information of each mobile and requires for this a synchronization of treatments.

To achieve this function, the method according to the first variant of the invention relies on a TDMA type waveform with a temporal segmentation of the channel: the signal received by the base station, as shown in FIG. 3 , is organized in frames, frame # 1 to frame #K, each comprising a determined number M of "bursts". Each "burst", conventionally allocated to a user thanks to spatial multiplexing is shared by several communications with the exception of one "burst" per frame which remains allocated specifically to a mobile. These periodic bursts called AMRS localization bursts are therefore allocated successively to all the space-time channels potentially usable on the frequency channel (by frequency channel is understood a pair of transmit / receive frequencies).

The structure of a "superframe", appearing in FIG. 3, corresponds to the period of updating of the spatial information of all the space-time channels, ie a number K of frames equal to twice the number of these channels (for each space-time channel, the spatial information is acquired over two frames: one for each of the frequencies of the frequency channel).

Depending on the duration of the "superframe" opposite the stationary spatial information, this method must be adapted by allocating for example more than one "burst" per frame to the AMRS location to reduce the updating period.

It is obvious that the choice of the number of localization bursts per frame has a direct impact on the capacities of the system. The synchronization of processing in this context essentially consists in directing the "bursts" received either towards the measurement of spatial information ("burst" of localization of an active mobile), or towards spatial demultiplexing ("burst" of traffic), or, either nowhere (unused location burst), and then distribute the spatial information to the transmit / receive multiplexing / demultiplexing filters according to the channel assignments and reassignments managed by the AMRS 13 controller. Figure 4b illustrates a functional diagram of the interface between the AMRS controller 13, the AMRS estimator 14 and the transmission and reception spatial multiplexers / demultiplexers 10 and 7.

The orientation of the "bursts" is carried out by means of a switch 15 receiving on a first input the signal received from the receiver 6, delimited by a discontinuous closed line, after transposition LF. The switch 15 also receives on a second input a control signal CTRL delivered by the AMRS controller 13. It includes a first, a second and a third output corresponding respectively to the "burst" of localization of an active mobile, to the "burst" traffic and unused location burst (mobile inactive). The first output is coupled to the input of the AMRS estimator 14 estimating the director vector Sj of the source i corresponding to a determined active mobile i. The estimated direction vector S _j is injected into the AMRS controller 13. The second output is inactive and the third output is coupled to the input of the spatial demultiplexer 7, delimited by a closed discontinuous line, consisting of the spatial filters Wj ^{1 "} , W ^ and Wg receiving respectively the same number N of spatial subchannels contained in the "burst" received traffic. "+" in exponent corresponds to the conjugate transposition function. The outputs of the spatial filters W *, W ^ and W3 are coupled respectively at the input of the demodulators 8i DEMOD # 1 to # 3, delimited by a closed discontinuous line, and deliver the information relating to the mobiles on the network of base stations represented in the figure by two parallel lines.

The reception weights of each coefficient of the spatial filters Wj ^{1 "} , W * and W * are updated using the directing vector S estimated by the AMRS 14 estimator and after control by the AMRS 13 controller.

In transmission, the modulators 11i, MOD # 1 to MOD # 3, delimited by a discontinuous closed line, respectively receive data from the network of base stations, to be transmitted towards the mobiles. Each modulated signal is injected respectively at the input of each spatial filter W,, W ₂ and W ₃ in transmission constituting the spatial multiplexer 10 delimited by a discontinuous closed line.

In the same way as in reception, an update of the weight in emission of the coefficients of the spatial filters W ₁ , W ₂ and W ₃ is carried out from the same directing vector S estimated by the AMRS estimator 14 and controlled by the AMRS controller. 13. The subchannels leaving respectively of each spatial filter W,, W ₂ and W ₃ are summed then emitted after transposition in intermediate frequency F | in the multi-channel transmitter 9 delimited by a discontinuous closed line.

The spatial filter suitable for transmission to a determined mobile is calculated from its director vector S estimated on the received signal. The need to keep the transmit and receive frequencies far enough apart, in particular to authorize the use of a common antenna base for the two transmit / receive directions of transmission, can make the direction vectors of the sources estimated on the signal received.

To solve this problem, a permutation of the frequencies of the same frequency channel (transmission / reception) is carried out by the method according to the first variant of the invention, leading at the level of the base station to a global permutation of the sub-bands. allocated to uplink and downlink. This permutation performed at the frame rate allows the estimation of the spatial information on the frequency used in transmission with an offset frame with respect to the reception, which means that in the "superframe" two consecutive "bursts" of location are used to make a complete estimate of the spatial information on each space-time channel. A frequency permutation controller 16 is described in the following description with reference to FIG. 8.

With spatial multiplexing, each channel, conventionally defined as the frequency and time support for a transmission between a base station SB and a mobile, is broken down into spatial subchannels. FIG. 5 illustrates a diagram of this decomposition where three channels X, Y and Z support the transmissions with respectively three mobiles MBx1, MBx2, MBx3, two mobiles MBy1, MBy2 and one mobile MBz1. FIG. 6 gives an illustration of the concept of frequency and time channel for the channels X, Y, Z in the case of uplinks and in the case of downlinks.

To perform a channel assignment, the method according to the first variant of the invention is based on an inter-mobile spatial correlation table.

This table, an example of which is presented in FIG. 7, contains the coefficients of spatial correlation CS of each of the mobiles with all the others within the fleet managed by the base station.

The spatial correlation coefficient CSij between two mobiles i and j is established from their directing vectors àfo, àp (estimated on the low frequency Ffc of the channel) and â _ιn , â; ^ (estimated on the high frequency F ^ of the channel ) according to the formula:

In the presence of multi-routes, the most powerful path vector associated with the direction of transmission on the downlink represents the spatial information representative of the mobile with regard to the channel assignment. In FIG. 7, the mobiles are grouped so as to show all of the spatial correlations inside each channel respectively for the X channel, the Y channel and the Z channel (areas surrounded by dotted lines) whose values are more particularly taken into account in the channel allocation method. The hatched lines and columns correspond to unused spatial subchannels.

With each new estimate of a director vector relating to an active mobile (after the analysis of each AMRS localization burst), the associated row and column of the table are updated and tests channel allocation are applied according to a determined allocation algorithm.

Its principle is as follows: an update of the distribution of the mobiles on the different channels of the cell is carried out every two frames after analysis of the two location bursts allocated to each mobile successively on the two frequencies of the duplex channel.

If the last measured spatial information is associated with a mobile entering the cell, the AMRS controller applies to the new mobile p the following admission test: for the mobile p to be admitted on the unsaturated channel Cn, it is necessary and ii suffices whatever the mobile x already present on one of the spatial subchannels of Cn:

CS _xp <Threshold (2)

if this condition is not fulfilled on any unsaturated channel (in relation to these potential capacities, that is to say to the maximum number of spatial subchannels), then the mobile cannot be supported by the base station.

Otherwise, the mobile is admitted on the Cn channel such as:

Max _xe c _n (CS _px ) _eCi (cS _py )] (3)

If the last measured spatial information is associated with a mobile p already present on the cell, then the AMRS controller begins by checking whether the mobile remains spatially decorrelated from the other mobile present on the same channel by application of the following test:

CS _xp (Threshold for all mobile x of channel C _n (4)

if this condition is met, the channel assignment is not changed. Otherwise, the AMRS control means tests the possibility to swap channel assignments between mobile p and mobile q on a different channel C _m . For this permutation to be possible, it is necessary and sufficient that the following two conditions are simultaneously fulfilled:

CSy _P (Threshold for any mobile and channel C _m (5)

CSq _X <Threshold for any mobile x of channel C _n (6)

If no permutation is possible, the mobile p can no longer be supported by the base station.

If, and this must be the most frequent case, several permutations are possible, the optimal choice criterion proposed is the following: the mobile q used to carry out the permutation with the mobile p is the one that minimizes the expression:

∑cs _{xp + ∑C} S py (7)

<€ C _n xe C _m x ≠ py ≠ q

where C _m designates the channel assigned to the mobile q. As with most spatial filtering techniques for multi-channel signals that do not use a learning sequence, the proposed method is only applicable if the transmission and reception chains introduce neither phase shift, differential gain nor distortions (non-linearity of amplification). It is very difficult and very costly to produce a device satisfying these constraints, this is why a method is described below for correcting by digital processing the drifts and distortions on the different transmission and reception channels.

The correction of the differential phase shifts and gain for each channel formed by each antenna of the antenna base 4 is carried out by a taring procedure broken down into two stages. This procedure is implemented by a device, a functional diagram of which is illustrated in FIG. 8. In a first step, the calibration of the reception chain 17i of each channel i comprising means for frequency transposition, filtering, amplification and analog / digital conversion, is carried out by injection upstream of the reception chain 17i a calibration signal, then adaptation of the coefficients of an equalization filter 18i coupled to the output of the reception chain 17i (except the first tap as a reference) making it possible to compensate for the dispersion of the impulse responses of the different channels i, by a taring analyzer 19 common to all the channels i formed by the antenna base 4. In a second step, the taring of the transmission chain 20i of each channel i comprising digital / analog conversion means, amplification, filtering and frequency transposition is carried out in a similar manner, also by injecting a calibration signal upstream of the transmission chain 20i. Part of the transmitted signal is fed back to the reception chain 17i, previously tared, via a resistive coupler 21 i. Finally, an equalization filter 22i coupled to the input of the transmission chain 20i is adapted according to the same principle as that of the reception chain 17i.

This figure also shows the controller 16 of the frequency permutation. A two-way switch transmits and receives respectively at the low frequency F5 and the high frequency F _n of the received signal. These two frequencies F5 and Fj-, being separated by means of a duplexer 24i disposed between the resistive coupler 21 i and the two-way switch 23i. The frequency permutation controller 16 Ft, and F h is coupled to the transmission and reception chains 20i and 17i of each channel i, to the taring analyzer 19 and to the two-channel switch 23i.

A first one-way switch 25i disposed at the input of the reception chain 17i receives on a first input the reception calibration signal, on a second input the signal sampled by the resistive coupler 21 i and on a third input the reception signal to the low frequency F5 or high frequency F _jη as a function of the position of the two-way switch 23i.

A second one-way switch 26i is coupled to the output of the reception equalization filter 18i and controls the calibration on reception. A third one-way switch 27i, disposed at the input of the transmission chain 20i before the equalization filter 22i receives on a first input the signal to be transmitted and on a second input the calibration signal on transmission.

The taring signal used is made up of N sinusoidal lines equally spaced in the useful band.

The principle of adapting the p coefficients of the equalization filters 22i and 18i of the transmission and reception chains 20i and 17i is based on the minimization of the following criterion:

where m'j = - l (Hj frequency response of channel i estimated at ^H i frequencies of the calibration signal), F. W _j is the frequency response of the equalization filter of channel i, with F matrix Nxp such that F (m, n) = e ^{J 'm "n} , and f _m one of the frequencies composing the calibration signal. The least squares solution for the equalization filter of channel i is therefore:

-1 w _{i =} F ⁺ .FF ⁺ .m '(9)

The channel formation in transmission as well as the independence of the sources mean that the signals to be transmitted in AMRS mode do not have a constant envelope and that their dynamics can exceed the range of linearity of the amplifiers of the transmission chains 20i.

To avoid unpaired distortions between channels, a pre-correction filter 28i is placed at the input of the transmission chain 20i and whose characteristics are as follows: by modeling the amplitude and phase distortions of an amplifier as following :

the pre-correction functions f and g 'established after learning the functions f and g are defined by:

W = G.Γ ¹ (11) I g '≈ -f'og

where G denotes a possible fixed gain of the pre-correction filter + amplifier assembly. The technique used to estimate the spatial information of mobile sources is one of the essential keys of this first variant of the invention. This very promising technique called "blind source separation" therefore exploits the non-Gaussian and independent character of the signals to be separated. The separation of blind sources makes it possible to take into account multi-paths correlated or not temporally in the estimation of the guiding vectors, which is not the case of the techniques conventionally applied in high resolution goniometry nor that of the separation techniques exploiting cyclostationarity . The temporally correlated multipaths are integrated into a single composite director vector while the decorrelated multipaths are separated by the method leading to the estimation of a director vector by independent path.

It is recalled that the algorithm for estimating spatial information is applied to signals in a single-emission configuration (on the location "bursts").

Treatments break down as follows:

- estimation of the source space (associated with time-decorrelated multipaths), - whitening of the source signals, and

- estimation of the bleached guiding vectors.

The estimation of the source space is carried out via a decomposition into eigenvectors, eigenvalues (QR method, of Jacobi or other) of the Hermitian correlation matrix of observations x (t):

R _y = E x (t) .x (t) ⁺ = UDU ^H (12)

where E x (t) .x (t) ⁺ corresponds to mathematical expectation, with U matrix of eigenvectors, and

D diagonal matrix of eigenvalues.

The correlation matrix of the source signals is then defined by

R _S = U _S .D _S .U _S ⁺ (13)

with U _s matrix of the eigenvectors of the source space, and D _s diagonal matrix of the eigenvalues of the source space.

The source space is isolated by applying a minimum threshold on the eigenvalues.

The source B bleaching matrix is written:

^B = ( ^R s) = D _S ^" > ² .U _S ⁺ (14)

The whitening of the signals then consists simply in applying the whitening matrix to the observation vector, which gives the whitened data for the following formula:

y = Bx = (R- ¹ ) .x (15)

The last step consists in estimating H corresponding to the unit matrix of the orthonormalized directing vectors of the sources. Several algorithms exist to perform this estimation among them is proposed that of COMON and CARDOSO-SOULOUMIAC the most robust tested, consisting in solving the following optimization problem: if we set z = H _mc ⁺ .y (16)

COMON proposes as estimator of H the unitary matrix H _mc minimizing the sum of all the squares of the modules of the crossed cumulants of order 4 of z, which amounts to finding the matrix H _mc maximizing the contrast factor defined by COMON namely:

M *

C _com = ∑ | Cum (z _j (t), Z _j (t) ^* , Z _| (t) ^* , Z _j (t)) | (17) i = l

(method detailed in the article by P. COMON: "Independent Component Analysis - Signal Processing", Vol. 36, N ° 3, Special Issue On Higher Order Statistics, pp 287-314, April 1994).

CARDOSO and SOULOUMIAC propose as an estimator of H the matrix H _mc minimizing the sum of the squares of the modules of cross cumulants of order 4 of z having different first and second indices, which amounts to finding the matrix H _mc maximizing the function C _because _ _SO u ^:

M ² ^w car -sou - ∑ | Cum (z _l (t), _{2 |} (t) *, 2 _k (t) *, z, (t)) | (18) i, k. l = 1

(method detailed in the article by J.F. CARDOSO and A. SOULOUMIAC "Blind Beamforming for Non Gaussian Signais", IEE Proc-F, Vol. 140, N ° 6, pp 362-370, December 1993).

The final estimate of the unbleached directeurs directing vectors used in spatial filtering is obtained simply by applying the inverse matrix of the whitening matrix:

Â = B ^_1 .H = U _S .D _S ^1/2 .H (19)

For spatial demultiplexing on reception, spatial filtering consists in optimizing for each mobile the antenna diagram as a function of its spatial information, that is to say by forming lobes in the direction of the multipaths of the target mobile signal and holes in the directions of the other mobile signals. The base station in AMRS mode therefore applies as many spatial filters as there are mobiles active on the same channel. The application of the spatial filter illustrated in Figure 4b comes down to the following formula:

where yj (t) represents the spatially filtered signal on which the contribution of the mobile was amplified and that of the other mobile strongly attenuated.

The proposed method for adapting the coefficients of the spatial reception filter is called estimated spatial adapted filtering, or estimated FAS, and consists of updating the spatial filter adapted to mobile i according to the estimated correlation matrix of the observations and of the spatial information according to the formula:

with: w; the weight vector adapted to the separation of the source i,

R _x = E [x (t) .x ⁺ (t) | = 1 ∑x (f). x ⁺ (f), (22) ⁿ k 1 ^ ^Fe ^ ^ ^Fe ^

estimation of the correlation matrix of observations,

m âi = ∑π _im â _im , (23)

P = 1

the composite directing vector of the mobile i constructed by summing the directing vectors of the multi-paths weighted by their relative powers, σj ^, the fictitious noise term added to make the estimation more robust with respect to the risks of rejection of the useful signal, linked to the errors committed on âj (the addition of this noise term is not crucial for the method of blind source separation, since the source vectors are directly and therefore precisely estimated from the signals received whereas in the case of goniometry each directing vector is deduced from an estimate of direction of arrival via calibration tables), and ld, corresponds to the identity matrix.

For spatial multiplexing in transmission, the principle of spatial filtering is to carry out the reciprocal operation of spatial filtering in reception, that is to say instead of separating signals arriving on the basis of antennas according to different azimuths, it is acts with this same base to generate a composite signal of which each component addressed to a particular mobile propagates in the direction defined by its principal directing vector. Unlike reception filtering where, to optimize the signal-to-noise ratio, it is important to take into account all the multi-paths from the same source, in transmission it is preferable to focus the energy only in the direction of the multi-path received the most powerful.

The application of the weights to the signals to be transmitted from the different modulators MOD # 1 to # 3 1 1 i as illustrated in FIG. 4b, is written as follows:

x = W.m (24)

with: m = (m- ^ t), rτi2 (t), ..., ιτ) M (t)) signals from M modulators, x signals transmitted on the N antennas,

W matrix of vectors Wj (i = 1 to M).

The method for adapting the coefficients of the spatial filter on reception is theoretically applicable in transmission, but due to the residual taring errors of the channels in transmission and in reception, so-called "feedback" errors are made which cause pointing errors with a bad positioning of the "holes" in the radiation diagram and the risk at the reception by the mobile of a bad Signal / Jammer ratio without possibility of rejection. This is why, the adaptation in emission is carried out according to a slightly different technique called synthetic FAS.

The calculation of Wj, spatial emission filter adapted to mobile i, is obtained by applying to its main directing vector (associated with the most powerful multi-path) the inverse, no longer of the estimated correlation matrix of the observations on the N antennas, but of a synthetic correlation matrix of the interfering signals R _jj :

Wj = R- ¹ .â (25)

This matrix is constructed from the directing vectors of two fictitious jammers positioned on either side (in azimuth) of each real jammer (each mobile constituting a jammer for all the others). The interest of this method is to allow a slight error on the direction vectors of the jammers by widening the "holes" of the radiation diagram around their estimated directions.

The synthetic correlation matrix used for the estimation of the vector of the weights W _j (focusing in the direction of the mobile i) is written in the form:

+1

^R Ji = Σ ^π J- ∑ ^a Jk- ^a f _k ⁺ 4- ld (26)

J ≠ i k = -1 k ≠ O

with: a ^ representing the directing vectors of the two fictitious jammers

a _jk = âj (0 + k.Δ0) (27)

In the absence of information on the azimuth of the source θ and on the variation of a direction vector with the azimuth of its source (without calibration table), these vectors are obtained by phase shift of the direction vector estimated at: (θ): â _jk = D _k . â _j (f5) (28)

with D ^ diagonal phase shift matrix whose diagonal coefficients are of the form:

d _k (i) = e ^j - ^MμNW (29)

or :

Δφ is a phase shift of the order of a few degrees to be adapted as a function of the base of antennas 4,

TIj designates the power of the source j considered as interferer in this case, this parameter is fixed at a value proportional to the depth of the "hole" which it is necessary to form in the direction of the moving j on the radiation diagram (typically 30 dB above the useful signal). σj ² is a noise term added to adjust the depth of the "hole" in the radiation diagram, its addition also has the consequence of making the matrix Rjj invertible and avoiding the use of an expensive computation of pseudo-inverse matrix. According to the second variant of the invention, a certain number of operations described above, in the first variant of the invention, are carried out differently and described below. These are the operations:

- estimation of the spatial information relating to each mobile which is carried out by means of operating methods of sequences known a priori

- isolation and demodulation of the signal received from each of the mobiles in connection with the base station to allow spatial demultiplexing.

The method according to the second variant of the invention is illustrated in FIG. 1 as in the case of the first variant of the invention. The method consists, from a multi-channel transmission / reception 1, of estimating 2 the spatial information relating to each active mobile source present in the cell at the two frequencies, carriers of the transmission and reception alternately, then from these information to make a optimal global multiplexing / demultiplexing 3 (time, frequency and space) for communications.

The general principle of the second variant of the invention is as follows: the spatial information is estimated for each mobile source present in the cell at the two frequencies of the channel, carriers of transmission and reception alternately, from a received signal. This spatial information is then used to adapt the coefficients of the spatial filtering structure in transmission. As regards the spatial demultiplexing and demodulation part, several variants are proposed by the second variant of the present invention:

- a FAS-DFE type structure (FAS, abbreviation for Filter

Adapted Spatial, and DFE, in Anglo-Saxon terminology for "Decision

Feedback Equalizer "), grouping a purely spatial filter (a complex coefficient per channel) and a decision-making body; - a FAST-BBT-DFE type structure (FAST, abbreviation for

"Spatio-Temporal Adapted Filter" and BBT abbreviation for White Noise

Temporarily, in Anglo-Saxon terminology "Decision Feedback

Equalizer "), consisting of a space-time filter associated with an independent decision-making body; - a so-called FAST-DFE structure consisting of a space-time filter coupled to a decision-making body.

While the first structure (FAS-DFE) uses to adapt the information estimated beforehand, or directly the learning sequence, the adaptation of the space-time filters implemented in the last two structures (FAST- BBT-DFE and FAST-DFE) directly use the known training sequences of the waveform.

The spatial information characterizing a mobile is defined by the directing vectors of the multipaths of the signal received on the basis of antennas. These directing vectors represent the response (amplitude and phase) of the antenna base to an incident signal along an azimuth characteristic of the position of the source.

The estimation 2 of the guiding vectors of each source uses signals received from the source of interest in a single-emission configuration. In other words in the waveform, a periodic time range, hereinafter called "burst", is allocated to each mobile for updating its spatial information. The method applied for this estimation 2 exploits the sequences known a priori and works perfectly in the absence of calibration of the antenna base. On the other hand, taking into account the generally large difference between the frequencies of the uplink (mobile to base station) and downlink (base station to mobile) frequencies, the estimate made on the received signals and used for spatial filtering in reception cannot be transposed for spatial filtering in transmission. This is why, in the method according to the first variant of the invention, a periodic permutation of the frequency groups of the uplink and downlink can be carried out so as to allow learning and updating of the spatial information also at the frequencies d 'program.

Most base stations manage several time / frequency channels in duplex mode and in this context the method according to the first variant of the invention can make it possible to ensure overall management of these channels within which spatial multiplexing generates AMRS subchannels so as to group preferentially on the same time / frequency channel the mobiles most spatially decorrelated. For each mobile, the estimated spatial information comprises one or more guiding vectors associated with the different detected paths as well as the relative power of each of the paths. From this data concerning all the mobiles whose transmissions are multiplexed together, a spatial filter is calculated in emission for each link with the constraint of focusing the radiation diagram in the direction of the main path of the useful signal and on the contrary of drilling the radiation pattern in the direction of the main path of each of the interfering signals (due to transmissions with other mobiles). The signals are formed by channel-by-channel summation of the outputs of the spatial multiplexing filters.

According to the variants implemented in the second variant of the invention, the spatial demultiplexing / demodulation assembly allows:

- FAS-DFE: to take into account the main useful path and to reject the main interfering paths and the other useful paths spatially decorrelated with the main path within the capacity limit structure (a structure of N sensors, can reject N-1 signals spatially decorrelated with the useful signal),

- FAST-BBT-DFE: to re-phase the energy of all the paths of the useful signal and to sub-optimally reject the interfering multi-path signals. While this method provides a gain in terms of signal-to-noise ratio on the current symbol compared to the FAS-DFE, it has the same capacities for rejection of interfering signals with the difference that useful multipaths other than the main path are not more assimilated to interfering signals, which frees as many degrees of freedom to take into account other interferers,

- FAST-DFE: to deal in a quasi-optimal manner with a scrambled multisensor signal by realizing not only the reshaping of the multipaths of the useful signal but also that of the multipaths of the interfering signals before their rejection. This method makes it possible to eliminate an interfering source from using only a single degree of spatial freedom whatever the number of multipaths according to which this source is received at the level of the multisensor network.

In addition, the method according to the second variant of the invention updates the coefficients of the spatial filters in reception and in transmission, performing respectively a spatial demultiplexing and a spatial multiplexing by taking into account the pairing faults, consequence of residual errors of taring of transmission and reception channels.

A device for implementing the method according to the second variant of the invention is shown diagrammatically in FIG. 2, as in the case of the first variant of the invention, and comprises the same subsets. However, a difference exists in the description of the second variant in that the spatial demultiplexer 7 comprises a determined number of spatial or spatio-temporal filters, coupled to a determined number of demodulators 8i equal to the maximum number of spatial channels fixed per frequency channel, for example three demodulators for a base comprising ten antennas.

The second variant uses the same notion of "superframe" illustrated in FIG. 3 and previously described. The interface between the AMRS controller 13, the AMRS estimator 14 and the transmit and receive spatial multiplexer / demultiplexer 10 and 7 is illustrated, not by FIG. 4b, but by FIG. 4a.

According to this FIG. 4a, the orientation of the "bursts" is effected by means of a switch 15 receiving on a first input the signal received from the receiver 6 delimited by a discontinuous closed line, after transposition LF. The switch 15 also receives on a second input a control signal CTRL delivered by the AMRS controller 13. It includes a first, a second and a third output corresponding respectively to the "burst" of localization of an active mobile, to the "burst" traffic and unused location burst (mobile inactive).

The first output is coupled to the input of the AMRS estimator 14 estimating the director vector S _j of the source i corresponding to an active mobile i determined. The estimated direction vector Sj is injected into the AMRS controller 13. The second output is inactive and the third output is coupled to the input of the space demultiplexer / demodulators 7 and 8i. The third output is also used for updating the space-time filters. The demultiplexer / demodulator 7 and 8i comprises N spatial or spatio-temporal filters not shown, receiving respectively the same number N of spatial subchannels contained in the "burst" traffic received. The outputs of the spatial or spatio-temporal filters are respectively coupled to the input of the demodulators 8i, and deliver the data relating to the mobiles on the network of base stations represented in the figure by two parallel lines. The reception weights of each coefficient of the spatial or spatio-temporal filters are updated using the director vector S estimated by the AMRS estimator 14 and after control by the AMRS controller 13.

In transmission, modulators 11 i MOD # 1 to MOD # 3, delimited by a discontinuous closed line, respectively receive data received from the network of base stations, to be transmitted towards the mobiles. Each modulated item of information is injected respectively at the input of each spatial filter in transmission, not shown, of the spatial multiplexer 10 delimited by a discontinuous closed line. In the same way as in reception, an update of the transmission weight of the coefficients of the spatial filters is carried out from the same directing vector S estimated by the AMRS estimator 14 and controlled by the AMRS controller 13. The sub-channels leaving respectively of each spatial filter are summed then emitted after transposition into intermediate frequency F | in the multi-channel transmitter 9 delimited by a discontinuous closed line.

The spatial filter suitable for transmission to a mobile is calculated from its director vector S estimated on the received signal. The need to keep the transmit and receive frequencies far enough apart, in particular to authorize the use of a common antenna base for the two transmit / receive directions of transmission, can make the direction vectors of the sources estimated on the signal received.

To solve this problem, a permutation of the frequencies of the same frequency channel (transmission / reception) is carried out by the method according to the second variant of the invention, leading at the level of the base station to a global permutation of the sub-bands. allocated to uplink and downlink. This permutation carried out at the frame rate allows the estimation of the spatial information on the frequency used in transmission with an offset frame with respect to the reception which means that in the "superframe" two consecutive "bursts" of location are used for perform a complete estimation of the spatial information on each space-time channel. A frequency permutation controller 16 controls the frequency permutation as described above with reference to FIG. 8.

With spatial multiplexing, each channel, conventionally defined as the frequency and time support for a transmission between a base station SB and a mobile, is broken down into spatial subchannels.

FIG. 5 illustrates a diagram of this breakdown according to the second variant of the invention in the same way as according to the first variant of the invention.

FIG. 6 gives an illustration of the concept of frequency and time channel according to the second variant of the invention in the same way as according to the first variant of the invention. To perform a channel assignment, the method according to the second variant of the invention is based on an inter-mobile spatial correlation table, an example of which is presented in FIG. 7 in the same way as according to the first variant of the invention . FIG. 8 provides a functional diagram of a switching and setting module of the device for implementing the method according to the second variant of the invention. The description of FIG. 8 is the same as that carried out for the first variant of the invention.

A device for implementing the method according to the second variant of the invention, shown diagrammatically in FIG. 2, implements a synchronization method specific to this variant.

The synchronization of the receiver on one of the transmission channels during the traffic phases (AMRS traffic bursts) is carried out in a scrambled environment (all mobiles sharing the same time / frequency channel transmitting simultaneously during the traffic bursts).

These reception conditions impose the implementation of a synchronization method more efficient than conventional single-sensor synchronization (threshold detector at the filtering output adapted to the learning sequence) ineffective in this context. The synchronization method according to the second variant of the invention was the subject of a French patent filed by the Applicant and published under the number 2,715,588, entitled: "Method and device allowing a modem to synchronize on a digital data transmitter over the air in the presence of a jammer ". It is implemented by an optimal multisensor detector under the following conditions:

- total noise (background noise + jammers) Gaussian,

- total circular noise (invariant by rotation),

- total white noise temporally (constant in the band, no multipath). The object of this detector is to make the decision between two hypotheses for each sample:

HO: x (t) = b (t) (noise only)

H1: x (t) = d (t- τ ₀ ). c (t) + b (t) (noise + signal) (30) with c (t) designating the multichannel channel supporting the transmission, d (t) the signal transmitted and b (t) the total noise of correlation matrix R.

The optimal detector in the sense of maximizing the probability of detection for a given probability of false alarm corresponds to the likelihood ratio under H1 and HO over the time interval [nrjT _e , ( ⁿ o ⁺ K _e ) T _e ] ( T _e sampling period) or:

_/ , ^ p (x (n ₀ + k), 1≤k <K _e / Hl)

Λ x (n ₀₊ k), 1 <k <K _e = ^H ; ; .Λ. * ..._ {(31)

P l ^x ( ⁿ o + k), 1 <k <K _e / HOj

where p (x / Hθ), p (x / Hl) denote respectively the probability density of the observation under HO, and H1.

The development of this analytical expression, under the assumptions defined above concerning total noise, leads to the following expression, function of x, c, b and R:

(32)

A statistic sufficient to solve the problem posed consists in subjecting the following estimate to a determined threshold η:

with:

1 K,

^R χ ( ⁿ 0) = 77 ^" Σ ^x ( ^{k + n} 0) ^x ( ^k + ⁿ 0) ⁺ . ^And (34) ^K ek = 1 fχd (no) = 77- ∑x (k + n ₀ ) d (k) ^* (35) ^κ e _{k = 1}

The spatial information characterizing the position of each mobile constitutes an essential parameter for the adaptation of the channel formation filters in transmission. This is therefore defined for each of the mobiles by the source vector associated with the main energy arrival on the basis of antennas.

This information is estimated on "bursts" allocated specifically and successively to each mobile and therefore in single-emission configuration (not scrambled).

For most cellular radio systems, standard channel models defining "typical" propagation conditions report a discrete impulse response corresponding to a number of paths. Consequently, for the estimation of spatial information, the modeling of the signal received by the antenna base is as follows:

P x (t) = ∑m (t- t _j ) a _{i +} b (t) (36) i = 1

where: x (t) = [x- ₎ (t), X2 (t), ..., XN (0], designates the signal observed by the antenna base, "T" in exponent defines the operation of transposition, m (t), designates the signal transmitted,

P, denotes the number of discrete paths and temporally decorrelated representing the impulse response of the channel, aj, denotes the director vector associated with the path #i, more precisely aj integrates the product of two components:

- the response of the antenna base to an incident wavefront of azimuth θ and site φ (vector with N complex coefficients),

- the response of the channel to the delay tj associated with the path #i (complex coefficient), (the source vectors being defined except for a complex coefficient, in the following description the two components are most often confused in the concept of source vector), b (t) = [b- | (t), b ₂ ( t) b _N (t)], designates the white Gaussian noise component on the N sensors. The principle of the estimation of the source vectors consists in extracting the outputs from a multi-sensor frame synchronization module. This module consists of N single-sensor correlators performing on each channel a filtering adapted to the learning sequence. In matrix notation this treatment is written:

y (t) = x (t). d * (- t) (37)

either for a sampled signal

1 ^L y (n) = f _xd (n) = -! ∑x (n + k) d ^* (k) (38)

^L k = 1

with y (k) the constituted vector of the N outputs of the correlators, d = [d (θ), d (l), ..., d (L - l), d (L -2) j, the learning sequence, and x (t) = [xj (t), X2 (t), ..., X | sι (t)], the signal observed on the N sensors.

The principal vector of the main path of the useful signal is therefore estimated by the output of the N correlators at the time of frame synchronization (maximum of the estimator of the multisensor detection function), that is:

= y (ti) (39)

with tj = - journey delay (composite or not) corresponding #i

F _e at the main peak detected on the detection function implemented by the multisensor synchronization process. There are other possible alternatives to this method of estimating spatial information which are compatible with the method which is the subject of the second variant of the present invention, namely:

- estimation by separation of blind sources at higher orders with a field of application limited to non-Gaussian signals,

- high resolution direction finding (with the additional constraint of having a calibrated antenna base).

The step of demultiplexing / demodulation on reception of the method according to the second variant of the invention is different from the step of demultiplexing / demodulation on reception of the method according to the first variant of the invention and consists, by means of a base antennas coupled to a multi-channel receiver and a digital signal processing unit, to separate and then demodulate the different components of the received signal, associated with mobile stations transmitting simultaneously and on the same frequency to the base station.

Several methods allowing demultiplexing followed by reception demodulation according to the second variant of the invention are described below as well as a filter structure adapted to each method.

These methods can be implemented using two types of filtering: spatial filtering or spatio-temporal filtering.

They all implement two identical consecutive digital treatments, namely:

- a multi-channel spatial or spatio-temporal filtering effecting the separation of the different components of the signal associated with the different active mobiles and the optimization of the signal / noise ratio on the current symbol, and

- a single-channel equalization / demodulation achieving the elimination of intersymbol interference and decision-making.

They have in common the fact that they exploit the a priori knowledge of learning sequences contained in the frames of the transmitted signal to adapt the coefficients of the filters used.

Three structures allowing the implementation of these methods, already introduced previously, and which are recalled below. - A first FAS-DFE structure, illustrated in FIG. 9, applies to spatial filtering associated with a DFE type equalization / demodulation module, encompassing two variants:

- "estimated" FAS -DFE, with adaptation of the spatial filter on the direction vector of the source of interest, and

- FAS "replica" -DFE, with adaptation of the spatial filter directly on the reference sequence (replica).

- a second and a third structure, a general structure of which is illustrated in FIG. 10, apply to space-time filtering associated with a DFE type equalization / demodulation module and comprise respectively:

- a FAST-BBT-DFE, illustrated in FIG. 11, with a decoupled structure, carrying out the anti-jamming and equalization / demodulation treatments, and the implementation of which is optimal in the presence of total noise (background noise plus interference) ) temporally white, and

- A FAST-DFE, illustrated in FIG. 12, performing jointly the spatial filtering processing and the equalization / demodulation function.

These different methods and structures for their implementation are described in detail below. Concerning the FAS-DFE, the purely spatial filtering consists in optimizing for each mobile the antenna diagram according to its spatial information directly from the reference sequence of the useful signal, that is to say by forming lobes in the direction of the multi-paths of the target mobile signal and holes in the directions of the other mobile signals. The base station in AMRS mode therefore applies as many spatial filters as there are mobiles active on the same channel.

The application of the spatial filter illustrated in Figure 9 comes down to the following formula:

where yj (t) represents the spatially filtered signal on which the contribution of the mobile was amplified and that of the other mobile strongly attenuated. This filtering method allows N-1 interference sources to be rejected (uncorrelated multipaths originating from the same jammer are all sources of interference to be taken into account). In the presence of multipaths of the useful signal, this method is not optimal because it does not allow phasing of the paths on the different channels before their summation. In return, its implementation does not require a large processing capacity.

The two proposed variants of adaptation of the coefficients of the spatial reception filter bear the name of "estimated" spatial adapted filtering or "estimated" FAS, and of "adapted replica" spatial filtering consist in updating the spatial filter to isolate the signal from the mobile. i, according to the formula:

- For the "estimated" FAS:

For the "replica" FAS:

with: w: the weight vector adapted to the separation of the source i,

estimation of the correlation matrix of observations,

m ^a i = ∑π _im â _im , (44)

P = 1

the composite directing vector of the mobile i constructed by summing the directing vectors of the multi-paths weighted by their relative powers, σ _j ² , the fictitious noise term added to make the estimate more robust with respect to the risks of rejection of the useful signal, linked to the errors committed on â _j (the addition of this noise term is not crucial for the blind source separation method, since the source vectors are directly and therefore precisely estimated from the signals received whereas in the case of goniometry each directing vector is deduced from an estimate of arrival direction via calibration tables ), and

1 ^L r _xd (rW∑x (n + k) d * (k) (45)

^L k = 1

Concerning the second structure relating to the implementation of the FAST-BBT-DFE method, the general problem of the adaptation on replica of a space-time filtering structure for a multisensor signal is defined theoretically as follows: either the received signal modeled by

x (t) = G (t). s (t) + b (t) (46)

where: x (t) = [x ₁ (t), X2 (t), ..., XN (0] designates the signal received on the basis of antennas,

G (t) = [gι (t), g ₂ (t), ..., g _N (t) j, the modeling of the channel on the N sensors, s (t) the signal emitted, and b (t) = [bj (t), b ₂ (t), ..., b _N (t)], the noise + interference component on the N sensors.

The problem posed consists in estimating the coefficients of the filter W of the space-time structure carrying out an optimal matching filtering to the multisensor signal.

The theoretical formulation of this filter is as follows:

W (t) = R- _b ¹ (t) - G (t) (47) with R _b (t) = E [b (t ₀ ), b ⁺ (t ₀ -t) correlation matrix of the noise component + interferer.

The estimation of this expression is not simple in the general case also the first proposed adaptation method (FAST-BBT) is placed in the restrictive hypothesis of a white noise in time which is mainly translated concerning the interfering signals by the following assumptions:

- the interfering signals are broadband (> useful signal band), - the interfering signals are single-path.

The problem to be solved is thus simplified by the form which the correlation matrix Rb takes.

R _b (t) = R _b r5 (t) with R5 constant. (δ (t) corresponds to the Dirac function)

If the frequency domain is taken into account W is written:

W (f) = R ^"1 G (f) (48)

Rb no longer depends on f and the problem is reduced to separate estimates of G and R5.

The G-channel estimate consists of N independent channel estimates on a single-sensor signal. Let g be one of the channels to be estimated, the single-sensor modeling of the received signal associated x (t) at the time of frame synchronization and sampled twice by symbol is as follows:

x (k) = g ^τ s (k) + b (k) (49)

where: s (k) = [s (kT _e ), s ((k -l) T _e ) s (k - (L -l) T _e )] denotes the samples of the known or replicated training sequence, and b (k), the sample of the noise + interference component. This equation, the unknown of which is g, is generally solved by methods minimizing the mean square error EQM defined by:

ξ = E ^χ OO - h ⁺ s (k) I with g = h * (50)

and whose theoretical solution is defined by

h - Rss ^r sx (51)

with R _ss s (t) s ⁺ (t) of which an unbiased estimate is given by:

and r 'S _ς X _γ = E s (t) x ^* (t) ^{' for} which an unbiased estimate is given by

₁ M

'SX = τ— ^ Y s (k) x * (k) (53)

( ^M - ^L ) n = L ₊ 1

In practice Rss exclusively dependent on the known training sequence priori, the matrix R _S s ^~ ^ P ^had to be precalculated.

The estimation of the correlation matrix of the noise + interference component R ^ is based on the knowledge of the training sequence and of the channel on the N sensors (matrix G). From the previous modeling of the multisensor signal, the expression of the estimate of the noise + interference component on the following channel n is deduced:

b _n (t) = x _n (t) - g _n (t). s (t) (54)

hence the expression of the estimate of the correlation matrix R5 -, M ^R b = 77 ∑ b (t ₀ + kT _e ) b ⁺ (t ₀ + kT _e ) (55)

^M k = 1

Several choices are possible for estimating W in particular for estimating the inverse of R ^ Among them is proposed a method based on ia decomposition into eigenvectors / eigenvalues of Rb, namely:

R _b = UDU ⁺ (56)

with U, matrix of orthonormal eigenvectors and D diagonal matrix of eigenvalues λj.

After this decomposition, the expression of W in the frequency domain becomes:

W (f) = UD ^_1 U ⁺ G (f) (57)

This decomposition of W makes it possible to identify the different processing steps involved in the filtering structure represented in FIG. 1 1. The expression of the filtered signal in the time domain therefore becomes:

y (t) = W ⁺ (-t) x (t) (58)

with W ⁺ (-t) = G ⁺ (-t) U ⁺ D ^_1 U (59)

The FAST-BBT-DFE method which has just been described therefore boils down to a suitable filtering on each channel not on the signal received directly but after a spatial bleaching pretreatment of its component: background noise + jammer; at the end of the processing chain, the channels thus formed are summed after weighting of each channel by a coefficient inversely proportional to the modulus of the eigenvalue of the correlation matrix of the noise component + associated jammer. The treatments are broken down sequentially as follows:

- estimation of channel on scrambled signals on each channel, - estimation of the correlation matrix of the noise component + interferer Rb, - estimation of the preprocessing matrix (matrix of the eigenvectors of the correlation matrix Rb),

- preprocessing: projection of the received signal and of the impulse responses of the channels estimated on the basis of the eigen vectors,

- filtering adapted to the channels projected on each channel to re-phase any multipaths,

- combinations of the different channels, each one being assigned a weight inversely proportional to the modulus of the corresponding eigenvalue so that the components corresponding to the jammers (maximum eigenvalues) are taken into account in the combination with a minimum weight and vice versa ,

- elimination of intersymbol interference and decision-making by a DFE processing module adapting to a criterion for minimizing the mean square error between "soft" decision and "hard" decision. The concatenation of processing and filtering constitutes a spatio-temporal filtering structure which differs from purely spatial filtering by its capacities to re-phase the decorrelated multipaths of the useful signal.

Although this method is sub-optimal, in the sense of the profitability of the antenna base, in the presence of multi-paths of the interfering signals, it has the advantage of not requiring long learning sequences (adaptation of the space filters). temporally performed independently on each channel at the preprocessing output), the dimensioning criterion for this parameter being the maximum temporal spreading of the channel.

Concerning the third structure relating to the implementation of the FAST-DFE adaptation method of a spatio-temporal filtering structure, no restrictive hypothesis concerning the statistical characteristics of the noise has been taken. Its principle consists in the joint optimization of a space-time filter and the recursive part of a decision equalizer in the loop (decision feedback equalizer, DFE) on a global criterion of minimization of the mean square error (EQM ) between the "soft" decision at the equalizer output and either the learning sequence (at the start of the process), or the "hard" decision (thereafter).

The various elements of this structure and their arrangement are shown in FIG. 12.

The signal at the equalizer output z (t) ("soft" decision) is therefore expressed as a function of the multisensor signal x (t) as follows:

NN _HR

2 (n) = ∑W _k ⁺ x _k (n) - £ HR ^* (l) z (n - l) (60) k = 1 1 = 1

where W [<designates the time filter applied on channel k, x _k (n) = [x _k (nT), x _k (nT + T _e ), ..., x _k (nT + (N _HR - l ) T _e )] designates the filter memory on track k.

The MSE, the minimization criterion adopted, is expressed in terms of the preceding expression:

This criterion is estimated according to the type of channel present - for a stationary channel:

² (62)

- for a non-stationary channel

with λ forgetting factor (0 <λ <1) to be adjusted according to the degree of non-parking of the channel. Many algorithms for estimating the set of filters (W | <with k = 1 to N, and HR) lead to each minimization of the MSE among which we can cite the recursive least squares algorithm (RLS in English), the gradient algorithms (Stochastic Gradient, Conjugated Gradients, etc.) and especially the "Recursive Modified Gram Schmidt" algorithm (described in the Telecom thesis of JL FETY) without doubt the current algorithm best suited to perform this estimation taking into account its speed of convergence and its numerical stability.

Simulations have confirmed the superiority of this method compared to the so-called FAST-BBT-DFE method in channel configurations presenting jammers with several paths (noise component + temporally correlated jammer).

However, this advantage has a cost in terms of the length of the reference sequence necessary to make the overall estimate of all the coefficients of the filtering structure converge.

The table below presents the main advantages and disadvantages of the methods presented above:

Depending on the problem to be addressed:

- configuration of useful routes,

- number and configuration of jammers, - length of the training sequence,

- number of sensors,

- possible means of treatment.

Analysis of the method presenting the best cost / performance compromise must be carried out.

Spatial multiplexing in transmission according to the second variant of the invention follows the same principle as that described in the case of the first variant of the invention with FIG. 4a as an illustration instead of FIG. 4b. The present invention applies more particularly to base stations although certain aspects of the method according to the invention which has just been described may find applications in the field of mobiles in particular with regard to increasing their sensitivity in reception. The principle of the first variant of the present invention is not limited to mobiles but can also be applied to fixed secondary stations remote from the base station.

The DFE equalizer implemented in the second variant of the present invention can be replaced by an equalizer according to the principle of maximum likelihood implementing the Viterbi algorithm.

Claims

1. Method for spatial multiplexing / demultiplexing of radio signals organized in frames and transmitted in duplex between at least one base station and several mobiles communicating on the same frequency and time channel by means of a receiver and a multichannel transmitter (1 ) integrated into the base station and coupled to an antenna base, characterized in that it consists, for non-Gaussian radio signals: - of estimating (2) the spatial information relating to each mobile from the signal received by the multi-channel receiver, for the reception and emission frequencies, by means of blind source separation methods, and from this information,

to isolate (3) by spatial filtering, whether or not there are multiple paths in the channel, the respective paths to each mobile whose power is greater than a determined threshold to allow spatial demultiplexing, and

2. Method according to claim 1, characterized in that the estimation (2) of the spatial information is carried out in a single-emission configuration, over periodic time ranges, arranged in a determined frame structure, and allocated specifically to the estimation of the spatial information of each mobile over two consecutive frames in order to take into account the two frequencies of the duplex transmission.

3. Method according to any one of claims 1 and 2, characterized in that it consists in permuting the transmission and reception frequencies for each frame to allow the acquisition of spatial information on the two frequencies when they are too distant so that this information can be transposed from one to the other,

4. Method according to any one of claims 1 to 3, characterized in that it consists in optimizing the efficiency of the multiplexing and spatial demultiplexing, in managing the allocation of the channels at the level of the set of frequency resources the and time allocated to the base station as a function of the movements of the mobiles, using a criterion of spatial correlation between mobiles integrating the spatial information acquired on the two frequencies used alternately for duplex transmission.

5. Method according to any one of claims 1 to 4, characterized in that the spatial filtering in transmission of the signal, intended for a determined mobile, is adapted from a synthetic correlation matrix of noise signal + jammers , established from pairs of fictitious jammers spatially arranged on either side of the mobiles in the direction of which the base station must not transmit this signal, so as to widen the holes "in the radiation pattern towards the jammers and by Consequently, the tolerance of the system to pointing errors consecutive to residual taring errors of the transmission and reception channels has to be increased.

6. Method according to any one of claims 1 to 5, characterized in that it consists in periodically applying a calibration procedure of the transmission and reception chains of each channel formed by the base of antennas and of pre- correction of amplification on transmission in order to limit pointing errors in transmission,

7. Device for implementing the method according to any one of claims 1 to 6, characterized in that it comprises:

- a base of transmit / receive antennas (4) coupled to switching and setting means (5),

a multi-channel receiver (6) comprising means for frequency transposition, amplification and analog / digital conversion, coupled at the output of the switching and setting means (5), a spatial demultiplexer (7), coupled at the output of the multi-channel receiver (6), comprising a determined number of spatial filters, each spatial filter forming a spatial channel,

a determined number of demodulators (8i) equal to the number of spatial channels determined by frequency and time channel, coupled at the output of the demultiplexer (7), and delivering on the network of base stations the data transmitted by the mobiles,

- a determined number of modulators (11 i) equal to the number of demodulators (8i), respectively receiving data received from the network of base stations and to be transmitted by the antenna base (4) intended for mobiles,

- a spatial multiplexer (10), coupled at the output of the modulators (11 i), comprising a determined number of spatial filters equal to the number of modulators (11 i), - a multi-channel transmitter (9) comprising digital / analog conversion means , of frequency transposition and amplification, coupled at the output of the spatial multiplexer (10), and in that it comprises:

- an AMRS digital processing module (12), comprising an AMRS controller (13) and an estimator (14) of the direction vectors of the paths relating to the mobiles communicating with the base station, enabling the weights of the spatial filters to be updated transmission and reception, management of transmission and reception frequencies, and commands for switching and setting means (5).

8. Device according to claim 7, characterized in that the taring means comprise for each channel (i), respectively comprising a transmission chain (22i) and a reception chain

(17i), and formed respectively by each antenna of the antenna base (4):

- a transmission signal equalization filter (22i) coupled to the input of the transmission chain (20i),

- an equalization filter (18i) of the reception signal coupled to the output of the reception chain (17i), - a switch at the input (25i) and at the output (26i) of the reception chain (17i), a switch (27i) at the input of the transmission chain (20i) and a two-way switch (23i) at the output of the transmission chain (20i), allowing the device to switch to the different operating modes: reception calibration, transmission calibration, transmission / reception,

- a coupler (21 i) arranged between the antenna (Ai) and the two-way switch (23i), making it possible to take part of the transmission signal to inject it at the input of the reception chain (17i) via the input switch (25i) of the reception chain (17i), and in that it comprises in common for all the channels (i):

a taring analyzer (19) allowing the analysis of the various taring signals arriving at the input (27i) and output (26i) switches respectively of the transmission (20i) and reception (17i) chains, and allowing to adapt the equalization filters (22i and 18i) of the transmission and reception chains (20i and 17i).

9. Device according to claim 8, characterized in that a pre-correction filter (28i) of the transmission chain (20i) is disposed between the equalization filter (22i) of the transmission chain (20i ) and the transmission chain (20i).

10. Device according to any one of claims 7 to 9, characterized in that it further comprises, for the permutation of the transmit and receive frequencies of the same frequency channel, a frequency permutation controller (16i), coupled respectively to the multi-channel receiver (6) and transmitter (9), and to the switching and setting means (5).

11. Method for spatial multiplexing / demultiplexing of digital radio signals organized in frames, comprising sequences known a priori, and transmitted in duplex between at least one base station and several mobiles communicating on the same frequency and time channel by means of a receiver and a multi-channel transmitter (1) integrated in the base station and coupled to an antenna base, characterized in that it consists: to estimate (2) the spatial information relating to each mobile, from the signal received by the multi-channel receiver, for the reception and transmission frequencies, by means of filtering methods, by exploiting the sequences known a priori, and on the basis of this information, - to isolate (3), whether or not there are multiple paths in the channel, the respective paths to each mobile whose power is greater than a determined threshold, and to demodulate the signal received from each of the mobile in conjunction with the base station, to allow spatial demultiplexing, and

12. Method according to claim 11, characterized in that it consists in isolating the main paths by spatial filtering.

13. Method according to claim 12, characterized in that the spatial filtering is implemented by a FAS structure associated with a decision and equalization member.

14. Method according to claim 11, characterized in that it consists in isolating the main paths by spatio-temporal filtering.

15. Method according to claim 14, characterized in that the space-time filtering is implemented by a FAST-BBT structure associated with a decision and equalization member.

16. Method according to claims 13 and 15, characterized in that the decision and equalization member is implemented by a DFE.

17. Method according to claims 13 and 15, characterized in that the decision and equalization member implements the Viterbi algorithm.

18. Method according to claim 14, characterized in that the space-time filtering is implemented by a FAST-DFE structure.

19. Method according to any one of claims 11 to 18, characterized in that the estimation of the spatial information is carried out in a single-emission configuration, over periodic time ranges, arranged in a determined frame structure, and allocated specifically to the estimation of the spatial information of each mobile over two consecutive frames in order to take into account the two frequencies of the duplex transmission.

20. The method of claim 19, characterized in that the estimation of the spatial information is carried out on the basis of the value taken by a multi-channel detection function of the sequence known a priori, at the optimal synchronization instant corresponding to the most powerful trip arrival time.

21. Method according to any one of claims 11 to 20, characterized in that it consists in permuting the transmission and reception frequencies for each frame to allow the acquisition of spatial information on the two frequencies when they are too distant so that this information can be transposed from one to the other,

22. Method according to any one of claims 11 to 21, characterized in that it consists in optimizing the efficiency of the multiplexing and spatial demultiplexing, in managing the allocation of the channels at the level of all the frequency resources and time allocated to the base station as a function of the movements of the mobiles, using a criterion of spatial correlation between mobiles integrating the spatial information acquired on the two frequencies used alternately for duplex transmission.

23. Method according to any one of claims 11 to 22, characterized in that the spatial filtering in transmission of the signal intended for a determined mobile is adapted from a correlation matrix noise + interference signal synthetic established from pairs of fictitious jammers spatially arranged on either side of the mobiles in the direction of which the base station must not transmit this signal so as to widen the holes "of the radiation pattern in the direction interferers and therefore increase the system's tolerance to pointing errors resulting from residual taring errors in the transmission and reception channels.

24. Method according to any one of claims 11 to 23, characterized in that it consists in periodically applying a taring and pre-correction procedure for amplification on transmission in order to limit pointing errors in transmission,

25. Device for implementing the method according to any one of claims 11 to 24, characterized in that it comprises:

a multi-channel receiver (6) comprising means for frequency transposition, amplification and analog / digital conversion, coupled at the output of the switching and setting means (5),

a spatial demultiplexer (7), coupled at the output of the multi-channel receiver (6), comprising a determined number of spatial or spatio-temporal filters, each spatial or spatio-temporal filter forming respectively a spatial or spatio-temporal channel,

- a determined number of demodulators (8i) equal to the number of spatial channels determined by frequency and time channel, coupled at the output of the demultiplexer (7), and delivering on the network of base stations the data transmitted by the mobiles, - a number determined of modulators (11 i) equal to the number of demodulators (8i), respectively receiving data to be transmitted by the base of antennas (4) intended for mobiles,

a spatial multiplexer (10), coupled at the output of the modulators (11 i), comprising a determined number of spatial filters equal to the number of modulators (11 i), - a multi-channel transmitter (9) comprising digital / analog conversion, frequency transposition and amplification means, coupled to the output of the spatial multiplexer (10), and in that it comprises: - an AMRS digital processing module (12), comprising an AMRS controller (13) and an estimator (14) of the direction vectors of the paths relating to the mobiles communicating with the base station, allowing the updating of the weights of the spatial filters on transmission and of the spatial or spatio filters -temporal ia reception, management of transmission and reception frequencies, and commands for communication and calibration means.

26. Device according to claim 25, characterized in that the calibration means comprise for each channel (i) formed respectively by each antenna of the antenna base (4):

- an equalization filter (18i) of the reception signal coupled at the output of the reception chain (17i), - a switch at the input (25i) and at the output (26i) of the reception chain (17i), a switch (27i) at the input of the transmission chain (20i) and a two-way switch (23i) at the output of the transmission chain (20i), allowing the device to switch to the different operating modes: reception calibration, transmission calibration, transmission / reception, - a coupler (21 i) arranged between the antenna (Ai) and the two-way switch (23i), making it possible to take part of the transmission signal to inject it at the input of the reception (17i) via the input switch (25i) of the reception chain (17i), and in that it comprises in common for all the channels (i): - a taring analyzer (19) allowing the analysis of the different taring signals arriving on the input (27i) and output (26i) switches respectively of the mission (20i) and reception (17i), and making it possible to adapt the equalization filters (22i and 1 Si) of the transmission and reception chains (20i and 17i).

27. Device according to claim 26, characterized in that a pre-correction filter (28i) of the transmission chain (201) is disposed between the equalization filter of the transmission chain (20i) and the broadcast channel (201).

28. Device according to any one of claims 25 to 27, characterized in that it further comprises, for the permutation of the transmit and receive frequencies of the same frequency channel, a frequency permutation controller (16i), coupled respectively to the multi-channel receiver (6) and transmitter (9), and to the switching and setting means (5).